The saliva liquefies the food for them to drink. But if fly vomit isn't bad enough consider this: Flies enjoy eating more than what's on your picnic table. They feast on nasty things like feces ...

He comes in every day to feed them a mixture of sugar water and watercolor paints, and they, in turn, cover his canvases with splotches of colored vomit. The painters are flies, and Knuth is taking ...